How to Winterize Your Boat: Complete Checklist

Skipping winterization is one of the most expensive mistakes a boat owner can make. A single freeze can crack an engine block, split water lines, and destroy raw-water pumps — repairs that easily run into the thousands. Proper winterization takes a few hours in the fall and saves you from catastrophic damage in the spring. This checklist covers every step, from the engine to the trailer, so nothing gets overlooked.

1. Fog the Engine

Fogging oil coats the internal components of your engine — cylinders, pistons, and valves — with a protective film that prevents corrosion during months of inactivity. For outboard and sterndrive engines, remove the air filter or flame arrestor, start the engine, and spray fogging oil into the carburetor or throttle body while the engine is running until it stalls. For fuel-injected engines, use the fogging oil port if your engine has one, or follow your manufacturer's specific procedure. This step alone prevents the most common form of winter engine damage: internal rust on cylinder walls from condensation.

2. Stabilize the Fuel

Untreated fuel breaks down over winter, leaving varnish and gum deposits in your fuel system that clog injectors and carburetor jets. Add a marine-grade fuel stabilizer to a full tank of fuel — filling the tank reduces the air space where condensation can form. Run the engine for 10 to 15 minutes after adding stabilizer so treated fuel circulates through the entire fuel system, including the lines, filter, and injectors. Ethanol-blended fuel is especially prone to phase separation in cold temperatures, making stabilizer essential rather than optional.

3. Drain All Water Systems

Water expands when it freezes, and any water left in your boat's systems will find the weakest point and crack it. Drain the engine cooling system completely. On raw-water-cooled engines, disconnect the hoses and let them drain. On closed-cooling systems, drain both the raw-water side and check the coolant level and condition on the closed side. Drain the livewell, washdown system, freshwater tank, hot water heater, and all associated lines. Open every drain plug and petcock. For lines that cannot be fully drained, pump non-toxic antifreeze (propylene glycol, not automotive ethylene glycol) through the system until it runs out the other end.

4. Remove and Store the Battery

Batteries left in a cold, unheated boat will slowly discharge and can freeze in extreme temperatures. A fully charged battery won't freeze until roughly minus 75 degrees, but a partially discharged battery can freeze at just 20 degrees — and a frozen battery is a destroyed battery. Disconnect the battery terminals (negative first), remove the batteries from the boat, and store them in a cool, dry location like a garage. Connect each battery to a quality trickle charger or battery maintainer for the duration of winter. Check electrolyte levels in flooded batteries and top off with distilled water if needed before storage.

5. Service the Trailer

Your trailer sits exposed to the elements all winter, and spring is a terrible time to discover that your bearings seized or your tires dry-rotted. Before storage, inspect wheel bearings and repack or replace them if they show any signs of wear, roughness, or contamination. Check tire pressure and inspect sidewalls for cracking. If the trailer will sit on pavement or concrete, place the tires on plywood or use jack stands to take the weight off the tires and prevent flat-spotting. Inspect the lights, wiring, and brake system. Apply grease to the coupler and winch gear. For more on keeping your trailer in top shape, see our trailer maintenance checklist.

6. Cover or Shrink-Wrap the Boat

A quality boat cover or professional shrink-wrap job protects your boat from snow, ice, rain, UV damage, and animal intrusion throughout the winter. If you use a fitted cover, make sure it's supported by a frame or support poles so water and snow don't pool on top and collapse the cover onto the boat. If you use shrink-wrap, ensure the installer includes ventilation openings to prevent moisture buildup and mold growth inside the wrap. Leave the drain plug out so any water that gets inside can escape rather than pooling in the bilge.

7. Indoor vs. Outdoor Storage

Indoor storage in a heated or climate-controlled facility provides the best protection but comes at a premium — expect to pay $30 to $60 per foot for the season depending on your area. Unheated indoor storage is more affordable and still shields the boat from precipitation, UV, and wind. Outdoor storage on a trailer in your yard or at a storage lot is the most economical option but exposes the boat to the full force of winter weather. If storing outdoors, invest in quality shrink-wrap and choose a location with good drainage so the trailer doesn't sit in standing water all winter.

Don't Skip the Details

A few additional steps round out a thorough winterization. Remove all valuables, electronics, and life jackets from the boat. Clean the interior thoroughly to prevent mold and mildew during storage. Spray exposed metal surfaces — throttle and shift cables, hinges, and hardware — with a corrosion inhibitor. Close all seacocks. And make a checklist of everything you removed or disconnected so spring recommissioning goes smoothly. When spring arrives, our spring boat prep guide walks you through every step to get back on the water safely.